The Benefit of UHR-CT: Precision of Repeated Volume Measurements of Pulmonary Nodules

Rationale: Ultra-high resolution computed tomography (UHRCT) produces radiological images with a spatial resolution of 0.25 mm in a matrix of 1024x1024. This should decrease measurement variation of nodule growth as a marker of malignancy, by making nodule delineation more precise for automatic volumetry segmentation and volume doubling time assessment than in conventional CT. If possible, this can shorten follow up of incidental pulmonary nodules to exclude malignancy, with less medicalisation and patient anxiety.

Objective: To assess the variability of semi-automated volume measurements of pulmonary nodules in patients with known or suspected pulmonary metastases on same-day repeated scans of equal radiation dose from two different CT scanners: CT scanner with standard spatial resolution (conventional CT, CT1) and UHRCT (CT2).

Study design: This is a single center prospective trial on 80 patients with known or suspected pulmonary metastases who are scheduled for chest and/or abdominal CT. Study participants will undergo two additional partial chest CT scans on either CT 1 or CT 2 for research purpose only, at similar radiation dose. Patients are equally divided across CT 1 and 2.

Study population: Patients who are 18 years or older with known solid pulmonary nodules compatible with metastases and who are willing and able to give informed consent are eligible. Patients are excluded if they have less than two eligible pulmonary nodules with a z range of 16 cm. Nodules with calcifications, surrounding opacities, or vessel- or pleural abutment will be excluded from analysis.

Main study parameters/endpoints: The main endpoint of this study is the upper limit of the 95% confidence interval of repeated semi-automated nodule volume measurements of both CT scanners.

Nature and extent of the burden and risks associated with participation, benefit and group relatedness:

CT imaging is associated with risks related to the use of ionizing radiation. The CT protocol including the scheduled CT scan and the additional scans in this study has been carefully designed to have a total radiation dose at the same level as the achievable diagnostic reference level of chest CT in the Netherlands, which is 542 mGycm in 2013 (1). The burden associated with the two extra study CT acquisitions comprises a dose length product (DLP) of 120.4 mGy•cm for research (1.7 mSv, which is lower than the background radiation of one year in the Netherlands, with a conversion factor of 0.014 from Deak et al (2)).

Inclusion criteria

• 18 years of age or older
• A solid primary tumour anywhere in the body and solid, noncalcified nodules in the pulmonary parenchyma on previous CT scans suspected for pulmonary metastases, according to radiological reports
• Two lung nodules that do not abut vessels or pleura with a two dimensional diameter between 5 and 10 mm within a distance of each other of 16 cm in the craniocaudal direction

Exclusion criteria

• Immobility (not able to stand up and get off the scanner table)
• Patients who received local pulmonary treatment: Radiotherapy, Excision, Ablation
• Patients with radiologically suspected lymphangitis carcinomatosa or consolidations around the nodules.
• Patients who only have calcified pulmonary nodules or nodules that abut vessels or pleura.